Voltage stability is an important index of power supply system, and voltage flicker caused by short fault can do much harm. When the flicker which is also known as interference electricity occurs, the solenoid-operated switch trips due to the loss of excitation, resulting in cut-off of power supply and significant economic losses to production system, data center, etc. Besides, override trip of control switch caused by short-circuit current is always a problem.
In order to resolve this problem, there are two means in the art: the mechanism with double contacts broke down separately, and the current limiting method involving magnetic reluctance caused by electric arc. However, these two means both have a disadvantage that, when instantaneous short circuit current occurs because of short-circuit fault, the circuit breaker does not trip so that current limiting cannot be realized.
In the mechanism with double contacts broke down separately, a resistance body is provided between the auxiliary contact and the main contact, and the main circuit passes through these two contacts to reach another side. When short-circuit fault occurs, the auxiliary contact breaks down at first, the main circuit passes through the resistance body and the main contact, and the produced prospective instantaneous short circuit current is limited in a range of the predetermined value by the resistance body. When the auxiliary contact breaks down, short circuit current is limited in a range under the effect of the resistance, and the main contact breaks down due to the limited short circuit current, whereby the electric arc of contact is controlled and the breaking capacity is improved. It is one existing means. It has a disadvantage that, once the short-circuit fault occurs, instantaneous peak short-circuit current occurs and results in voltage drop and voltage flicker (interference electricity). The most serious problem caused by peak short-circuit current is the override trip problem, which is a safety problem that cannot be ignored.
In the short-circuit current limiting method involving magnetic reluctance caused by electric arc, when the short-circuit fault occurs, the contact breaks down and the breaking arc generates arc magnetic field, so that the magnetic field force restrains the growth of electric arc and thus short circuiting arc is restrained. It has a disadvantage that, once short-circuit fault occurs, instantaneous peak short-circuit current occurs and results in voltage drop and voltage flicker (interference electricity). The most serious problem caused by peak short-circuit current is the override trip problem, which is a safety problem that cannot be ignored.
That is, the existing circuit breaker trips in such a manner that the main contact and the auxiliary contact break down separately. Since a resistance is connected in series between the auxiliary contact and the main contact, the tripping may be realized only when short-circuit fault occurs. However, in this situation, drop-away current limiting is realized after voltage flicker caused by short-circuit current happens. Also, in the circuit breaker which uses electric arc to limit short-circuit current, voltage flicker happens before the tripping, and drop-away current is limited by contact arc after the tripping.
As to the power supply circuit, short-circuit fault is very dangerous. The circuit-breaker, which solves short circuit breaking problem, does not solve the existing voltage flicker problem. The flicker problem and override trip problem are most serious problems of the power supply system, which may result in forced outage, breaking off of big data exchange operation, breaking down of important equipment, shutting down of production line, etc. In order to eliminate flicker in power grid, short-circuit current should be stably limited in a range without peak value during the entire short-circuit fault.